1. Field of the Invention
The present invention relates to an apparatus for and a method of forming a synthetic resin product such as an automotive instrument panel or the like according to a vacuum forming process.
2. Description of the Related Art
It has been a conventional practice to shape a synthetic resin sheet with a vacuum forming mold and then trim off unnecessary portions from the shaped sheet. Japanese laid-open utility model publication No. 56-149617 discloses a vacuum forming apparatus of the draping type which has a hot trimming cutter. The disclosed vacuum forming apparatus simultaneously forms and trims a thermoplastic sheet. The hot trimming cutter has a built-in heater for melting and cutting off the thermoplastic sheet.
If a thermoplastic sheet to be shaped by the conventional vacuum forming apparatus comprises a laminated sheet having a foamed layer, however, since the foamed layer is resilient, the foamed layer may be dragged in a trimming direction by the trimming cutter as it moves to trim the thermoplastic sheet, possibly preventing the thermoplastic sheet from being cut off. Since the heater of the hot trimming cutter heats the thermoplastic sheet with heat, the thermoplastic sheet may not be clearly cut to a desired shape, but may be burred at the severed edge. If a shaped thermoplastic sheet is used as an automotive instrument panel, for example, it has many openings for installing various components such as an aid-conditioner component, etc. Burred edges of the openings prevent such various components from being properly installed in the openings.
The foamed layer of the thermoplastic sheet has substantially spherical cells containing air therein. Depending on the direction or angle in which the trimming cutter cuts off the thermoplastic sheet, some of those cells in the foamed layer are broken, reducing the quality of the thermoplastic sheet. Alternatively, while the thermoplastic sheet is being severed by the trimming cutter, cells may be displayed or deformed by the trimming cutter, preventing the trimming cutter from imparting appropriate shearing forces to the thermoplastic sheet.